Wireless communications have become ubiquitous in modern society. Cellular networks have matured and now provide extensive coverage for voice communications, and are being increasingly used for data and media applications. However, data rates for cellular networks are relatively low, and thus are limited to those applications that do not require high data rates, such as basic Internet browsing, email, text messaging, and low resolution audio and video streaming. Although such applications are useful, consumers are demanding richer media experiences that require significantly higher data rates, such as those provided by broadband service providers. Broadband access is typically provided by cable and telephone service providers through hard-wired cable, digital subscriber line (DSL), T1, or T3 connections. Wireless access points may be coupled to the hard-wired connections to provide local wireless zones, or hotspots, in which mobile stations with complementary communication capabilities are afforded wireless broadband access.
The Institute for Electrical and Electronics Engineers (IEEE) has set forth a widely used local wireless communication standard, which is referred to as the IEEE 802.11 standard or Wireless Fidelity standard (WiFi). Unfortunately, a WiFi access point has a very limited range of at most 100 to 300 feet, depending on environmental conditions. Given WiFi's limited range, continuous coverage throughout a large geographic area is impractical, if not impossible. As such, mobile users only get the benefit of wireless broadband access when they are within a WiFi hotspot, which is inherently limited in size.
To address the limitations of WiFi and provide continuous broadband access over much larger areas in a fashion analogous to the coverage provided by cellular networks, the IEEE has set forth a next generation wireless communication standard, which is referred to as the IEEE 802.16 standard or wireless metropolitan area network standard (WiMAN). As the IEEE 802.16 standard has evolved, it has been referred to more frequently as the Worldwide Interoperability for Microwave Access standard (WiMAX). WiMAX promises to extend the wireless broadband access provided by a single access point up to 30 miles for fixed stations and three to ten miles for mobile stations.
Given the extended range provided by WiMAX systems, the access points are generally referred to as base stations. Although these base stations provide broadband access over much larger areas, environmental conditions may limit access in certain areas within a given coverage area. For example, geographic elements, such as hills or valleys, may limit access within a coverage area. Buildings or other man-made structures may also affect access throughout a coverage area. Further, access within buildings or mass transit vehicles, such as buses, trains, boats, and the like, may be completely blocked, if not severely limited.
To address these areas of limited access within a coverage area of a base station, one or more relay stations may be employed to effectively extend the reach of the base station. Instead of the base station communicating directly with a mobile station or fixed station of an end user, the relay stations may act as liaisons between these stations and the base station. One or more relay stations may be provided between these stations and a given base station, depending on the needs of the communication environment. The base station and the relay stations use wireless communications to communicate with each other, and the last relay station in the relay path will communicate with the mobile or fixed stations. In addition to addressing dead spots in a given coverage area of a base station, relay stations may also be used to further extend the coverage area of a base station. In most instances, relay stations are less complex and expensive than base stations; therefore, using relay stations to extend the coverage area of a single base station is more economical than installing additional base stations and the infrastructure needed to connect the base stations to a core communication network.
Relay stations may be fixed or mobile. For example, certain relay stations may be permanently affixed to or inside a building, whereas other relay stations may be mounted inside different cars of a subway train. To provide continuous coverage in a coverage area of a given base station, access provided to a mobile station may be transitioned from one relay station to another relay station, from the base station to a relay station, or from the base station to a relay station as the mobile station moves throughout the coverage area of the base station. Access may also be transitioned from one base station to another or from a relay station associated with a first base station to a relay station associated with a second base station as the mobile station moves from one location to another. Similarly, moving relay stations may transition from one base station to another as they move from one location to another.
An issue arising from the use of relay stations is the inability to effectively control quality of service (QoS) for communications that are supported, at least in part, through one or more relay stations. QoS generally relates to metrics, such as delay, jitter, or data loss, that impact the quality of a given communication session or access in general. When a base station communicates directly with a mobile station over an air interface, it is relatively easy for the base station and the mobile station to cooperate with one another to both determine the communication conditions of the air interface and take steps to ensure a given level of QoS is maintained. However, the addition of one or more relay stations in the communication path significantly complicates QoS control, because there are two or more air interfaces between the base station and fixed or mobile stations, which are communicating with the relay stations. To further complicate matters, the conditions of these air interfaces may change dynamically, especially when moving relay stations are involved.
The IEEE 802.16j standard addresses the use of relay stations and the control of communications over the multiple, wireless communication hops between a base station and a fixed or mobile station through one or more relay stations. However, IEEE 802.16j has not yet provided an effective and efficient way to provide QoS controls when relay stations are involved. As such, there is a need for a technique to provide QoS control when relay stations are used in wireless communication environments.